Defect Structure of Y-Doped Ceria on Different Length Scales

Abstract

An exhaustive structural investigation of a Y-doped ceria (Ce1–x Y x O2–x/2) system over different length scales was performed by combining Rietveld and Pair Distribution Function analyses of X-ray and neutron powder diffraction data. For low doping amounts, which are the most interesting for application, the local structure of Y-doped ceria can be envisaged as a set of distorted CeO2- and Y2O3-like droplets. By considering interatomic distances on a larger scale, the above droplets average out into domains resembling the crystallographic structure of Y2O3. The increasing spread and amount of the domains with doping forces them to interact with each other, leading to the formation of antiphase boundaries. Single phase systems are observed at the average ensemble level.

Pigments based on terbium-doped yttrium cerate with high NIR reflectance for cool roof and surface coating applications

“…As the terbium concentration increases, the intensity of C-type reflections are more prominent. This result is in agreement with the reported literature as heavily doped higher ionic radii for cerium strongly influence the structural transformation from a fluorite to a C-type structure [37]. The introduction of terbium into Y 2 Ce 2 O 7 slightly shrinks the lattice, which is evident from the shift in diffraction peaks to higher 2q angle in comparison with the host (Inset of Fig.…”

Structural characterization of Tb- and Pr-doped ceria

“…The best performances are generally observed for those dopants (Gd, Sm, Y) that minimize the size mismatch with the host Ce +4 , thus reducing defects aggregation and facilitating the diffusion process [1]. The increase of the doping amount above a certain critical threshold, around x = 0.20 [1], otherwise produces dopant rich nanodomains [2,3], with the tendency of the dopant, probed by EXAFS [4][5][6], NMR [7] and PDF [3,8], to retain the local environment as in its pure oxide. Another common feature of all doped-ceria systems is the presence of~8-fold coordinated Ce in the +4 state and~7-fold coordinated dopant ions in the +3 state [4,9].…”

Size and spatial correlation of defective domains in yttrium-doped CeO2

“…At μ = 0.250 already, the value of x(M2) refined by the two-phase model is close to that in Y 2 O 3 despite the fluorite average structure of this sample. This limited spatial extent over which C-type and fluorite interatomic distances are described by the two-phase model was defined as "droplet" (Scavini et al, 2012;Coduri et al, 2013a). As a result of both the tiny coherence length and random orientation, droplets average out to zero in the reciprocal space and do not constitute a secondary phase in the XRPD patterns.…”

“…To overcome some of those drawbacks, we recently exploited the pair distribution function (PDF) method to investigate doped ceria compounds upon doping with Gd (Scavini et al, 2012), Y (Coduri et al, 2012a(Coduri et al, , 2013a, and other rare earths (Coduri et al, 2012b(Coduri et al, , 2014, also under fuel cell operating conditions (Coduri et al, 2013b). The advantage of the PDF analysis over EXAFS lies in that the PDF function [i.e.…”

“…• At intermediate dopant concentration (0.25 ≤ μ < 0.50), the dopant-rich droplets average out to C-type (dopant oxidelike) "domains", the size of which spans some hundreds of Ångstroms (Coduri et al, 2013a). …”